(a) Field of the invention:
The present invention relates to a mechanical fuel injection device for injection carburetors capable of adequately adjusting fuel injection rate on the basis of negative pressure produced depending on flow rate of air to be aspirated.
(b) Description of the prior art:
A fuel injection device of this type has already been proposed by the inventor et al. of the present application. This fuel injection device will be described below with reference to FIG. 1. The fuel injection device consists of an air section of regulator 2 and a fuel section of regulator 3 which are arranged opposedly to each other on both the sides of a suction tube 1 of a carburetor. The interior of the air section of regulator 2 is devided by a first diaphragm 4 into a depression chamber 5 into which negative pressure is applied through the venturi of the carburetor and an air chamber 6 which is communicated with atmosphere. On the other hand, the interior of the fuel section of regulator 3 is divided by a second diaphragm 7 into a fuel pressure chamber 8 into which a fuel is supplied and a fuel injection chamber 9. The fuel pressure chamber 8 and the fuel injection chamber 9 are communicated with each other through an orifice or metering jet 10. The first diaphragm 4 and the second diaphragm 7 are connected to each other by a connecting member extending across the suction tube 1, and formed on the connecting member 11 is a fuel injection valve 11a which is capable of opening and closing a fuel injection port 9a formed in the fuel injection chamber 9 for adjusting the degree of said port.
This fuel injection device functions as described below. When the engine starts and air is drawn into the suction tube 1, negative pressure of a level corresponding to the air flow rate is produced in the venturi. Under this negative pressure, the first diaphragm 4 is displaced and the connecting member 11 is shifted together therewith, thereby opening the fuel injection port 9a. Since the degree of opening of the fuel injection port 9a is determined by the degree of displacement of the first diaphragm 4 or the connecting member 11, the fuel is ejected from the fuel injection port 9a in a quantity corresponding to the air flow rate. So long as the air flow rate remains constant, the air section of regulator 2 is balanced with the fuel section of regulator 3 in this condition and the fuel is continuously ejected at the rate determined as described above.
This mechanical conventional fuel injection device requires, for enchanced fuel control accuracy, a large and high precision fuel control unit which consists of the air section of the regulator, the fuel section of the regulator and the connecting member, and when the fuel injection system has the conventional structure, it must be equipped with a fuel control unit adapted for controlling low fuel flow rates in a slow driving range and another fuel control unit adapted for controlling high fuel flow rates in a main driving range, thereby presenting problems in that the fuel injection device is inevitably enlarged in the structure and that manufacturing cost for the fuel injection device becomes expensive.